<div class = "top_menu">
	<?php
		if (isset($_SESSION['username'])) {
	?>
		<a href = "index.php"> Main page </a> |
		<a href = "showusers.php"> Registered users</a> |
		<a href = "showdevices.php"> Placed devices</a> |
		<a href = "showavailabledevices.php"> Available devices</a> |
		<a href = "howto.php"> How to work </a>
	<?php
		} else {
	?>
		Some information about what for this site is created
	<?php
		}
	?>
</div>